Psychedelic drug, also called psychotomimetic drug or hallucinogen , any of the so-called mind-expanding drugs that are able to induce states of altered perception and thought, frequently with heightened awareness of sensory input but with diminished control over what is being experienced. See alsohallucinogen.

One of the most common psychedelic drugs is d-lysergic acid diethylamide, or LSD-25, which was synthesized in 1938 by a chemist working for Sandoz Laboratories in Switzerland. LSD proved to be an extraordinarily powerful drug, hundreds or thousands of times more powerful than other substances such as mescaline and psilocin and psilocybin. LSD may induce sympathomimetic effects, such as an increased heart rate, but has not been shown to cause death directly. Chronic exposure, however, may lead to psychoses or difficulties with memory or abstract thinking. Although their effectiveness has not been proved, psychedelic drugs have been proposed as treatment aids for psychotherapy, alcoholism, and mental disorders. The actual mechanisms of the drugs are not fully understood, but these and other popular mood-altering substances appear to work by mimicking or supplanting the effects of naturally occurring neurotransmitters. LSD has a chemical resemblance to serotonin, imbalances in which have been associated with various problems of mind and mood, such as depression, obsessive-compulsive disorder, and schizophrenia. However, research has shown that LSD experiences involve neither true hallucinations nor actual schizophrenic or psychotic episodes.

Psychedelic drugs achieved their widest popularity during the 1960s and early ’70s, when drugs such as LSD were central to the “hippie” subculture in western Europe and the United States. Although the drugs diminished in popularity, they retained a following in some regions and cultures and achieved renewed popularity during the 1990s, when LSD and Ecstasy had a significant youth following in the United States and Europe.

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substance that produces psychological effects that are normally associated only with dreams, schizophrenia, or religious exaltation. It produces changes in perception, thought, and feeling, ranging from distortions of what is sensed (illusions) to sensing objects where none exist (hallucinations)....

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All these terms are borrowed from medicine and are closely identified with pathology. In this sense, all are negative. It has been suggested that these drugs be called psychedelic (“mind manifesting”). This term shifts the emphasis to that aspect of the drug experience that involves an increased awareness of one’s surroundings and also of one’s own bodily processes—in brief,...

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